This invention relates to controlled rectifiers employing ring gates and more specifically relates to a novel structure which permits selection of gate sensitivity and to a novel gettering structure for reducing leakage currents and improving blocking characteristics.
Controlled rectifiers employing an auxiliary cathode to permit firing of the device from a very low input gate current are well known and are shown, for example, in U.S. Pat. No. 3,586,827 in the names of Thomas J. Roach and James H. Hauck, and assigned to the assignee of the present invention.
Controlled rectifiers employing a ring gate are also well known. Devices of this type can employ an auxiliary cathode region. A portion of the ring gate acts as an auxiliary cathode of an auxiliary controlled rectifier, as well as the main gate for firing a main emitter region contained within the periphery of the ring gate. An auxiliary gate is commonly provided laterally exteriorly of the auxiliary emitter region and is partially covered by the ring gate.
Once the geometry of the auxiliary gate is fixed relative to the auxiliary emitter and portions of the ring gate, the sensitivity of the device is also fixed. The spacing between the auxiliary gate and certain portions of the ring gate determines the sensitivity of the device. That is to say, when the auxiliary gate is very close to certain portions of the ring gate, the sensitivity to turn-on is very low. If, however, greater spacing is used, the device is more sensitive. In present devices, once the device structure is completed, gate sensitivity is fixed and cannot be altered.
It is also known that phosphorus can be used as a getter for impurities and defects in silicon and thus will increase the lifetime of minority carriers in the device. However, phosphorus gettering is normally effective only within the main emitter region when an N-type emitter region is formed within a P-type gallium region by phosphorus diffusion. The area external of the emitter region, however, does not benefit from the phosphorus gettering, and the lifetime of minority carriers in the external device area is very short, so that the blocking characteristics of the device may be poor.